The present invention relates to a line-scanning optical printer, in which sensitized paper is scanned by means of a scanning head so that the sensitized paper is exposed to a linear light with a given width and length projected from the scanning head, whereby an image is formed.
Video printers are spread as a type of line-scanning optical printers, whereby a digitally processed image on a display is printed on a sensitized sheet. The video printers may be based on any of print systems including a thermal system, ink jet system, laser beam scanning system, liquid crystal shutter system, etc. Among these systems, the liquid crystal shutter system is watched as the best suited one for a small-sized, lightweight printer. An example of a video printer of the liquid crystal shutter type is disclosed in Japanese Patent Application Laid-open No. 2-287527.
The disclosed video printer will now be described with reference to FIG. 21.
A casing 101 contains therein a film loading portion 102 for holding a film pack FP that is stored with a large number of self-processing films F. Further, conveyor roller means 106 is located adjacent to an aperture 103 of this film loading portion 102. The conveyor roller 106 is composed of a pair of rim drive rollers 104a and 104b, which holds therebetween and draw out a specified film F from the film pack FP in the film loading portion 102, and a pair of squeezing rollers 105a and 105b for developing the film F after exposure for recording.
An exposure recording portion 107 for forming an image on the film F is located between the rim drive roller pair 104a and 104b and the squeezing roller pair 105a and 105b. The exposure recording portion 107 includes a light source 108 such as a halogen lamp. The film F is exposed to light emitted from the light source 108 and transmitted through an optical fiber bundle 109, a color filter (not shown) having three colors, R, G and B, which are arranged parallel to one another in an image sub-scanning direction, a liquid crystal light bulb 110, and a refractive index distribution lens array 111.
Polarization plates are arranged individually on the upper and lower surface portions of the liquid crystal light bulb 110, having their deflecting directions in parallel relation. On the other hand, a first glass substrate is located inside the polarization plates. The color filter (not shown), having thin films of three colors, R, G and B, deposited thereon by vacuum evaporation, is formed on one surface portion of the first glass substrate, while a plurality of pixel electrodes, in which transparent electrodes are linearly arranged along the color filter (not shown), that is, in the sub-scanning direction, are formed on the other surface portion.
A liquid crystal, such as a twisted nematic liquid crystal, is sealed between the pixel electrodes and a second glass substrate. In this case, a common electrode, a transparent electrode, is formed on the second glass substrate side of a boundary surface between the second glass substrate and the liquid crystal by vacuum evaporation. The polarization plates are arranged on the other surface portion side of the second glass substrate. Light transmitted through the polarization plates passes through the refractive index distribution lens array 111, whereby the film F is exposed.
As described above, the conventional line-scanning optical printer is designed so that the film F is exposed to the light emitted from the light source 108 and transmitted through the color filter (not shown) having three colors, R, G and B, which are arranged parallel to one another in the image sub-scanning direction, the liquid crystal light bulb 110, and the refractive index distribution lens array 111 by means of the optical fiber bundle 109. With this arrangement, not only the members constituting the optical system are costly but also assembling involves a number of complicated processes thereby increasing the total cost of the apparatus.
Conventionally, therefore, avoiding the use of a costly optical fiber bundle, there has been used an optical device manufactured by utilizing an optical system that is composed of a lens, concave mirror, flat mirror, etc., which can be formed of plastics at low cost. According to this conventional optical device, however, an image is formed on a sheet by utilizing a spot light source, so that the quantity of light emitted from the spot light source cannot be distributed uniformly. Thus, unevenness in brightness is caused such that the central portion of the spot light source is brighter than the peripheral portion.
The object of the present invention is to provide a line-scanning optical printer capable of obtaining uniform-density images without entailing unevenness in brightness, incorporating a low-cost optical device constituting an optical system made available with low-cost constituent members and reduced number of assembly processes.
In order to achieve the above object, a line-scanning optical printer according to the present invention, which is designed to form an image on a sensitized material by projecting a linear light having a given width and length thereto while successively scanning individual lines in the direction of the width, comprises a casing having light shielding properties and including a window portion for radiating the linear light to the outside, a light emitting element which substantially functions as a point light source and is stored in the casing, an optical system for guiding light from the spot light source or light emitting element as the linear light to the window portion, and a liquid crystal optical shutter attached to the window portion.